text: // SPDX-License-Identifier: GPL-2.0-only
  /* (C) 1999-2001 Paul `Rusty' Russell
   * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
   * (C) 2006-2010 Patrick McHardy <kaber@trash.net>
   */
  
  #include <linux/types.h>
  #include <linux/timer.h>
  #include <linux/netfilter.h>
  #include <linux/in.h>
  #include <linux/icmp.h>
  #include <linux/seq_file.h>
  #include <net/ip.h>
  #include <net/checksum.h>
  #include <linux/netfilter_ipv4.h>
  #include <net/netfilter/nf_conntrack_tuple.h>
  #include <net/netfilter/nf_conntrack_l4proto.h>
  #include <net/netfilter/nf_conntrack_core.h>
  #include <net/netfilter/nf_conntrack_timeout.h>
  #include <net/netfilter/nf_conntrack_zones.h>
  #include <net/netfilter/nf_log.h>
  
  static const unsigned int nf_ct_icmp_timeout = 30*HZ;
  
  bool icmp_pkt_to_tuple(const struct sk_buff *skb, unsigned int dataoff,
  		       struct net *net, struct nf_conntrack_tuple *tuple)
  {
  	const struct icmphdr *hp;
  	struct icmphdr _hdr;
  
  	hp = skb_header_pointer(skb, dataoff, sizeof(_hdr), &_hdr);
  	if (hp == NULL)
  		return false;
  
  	tuple->dst.u.icmp.type = hp->type;
  	tuple->src.u.icmp.id = hp->un.echo.id;
  	tuple->dst.u.icmp.code = hp->code;
  
  	return true;
  }
  
  /* Add 1; spaces filled with 0. */
  static const u_int8_t invmap[] = {
  	[ICMP_ECHO] = ICMP_ECHOREPLY + 1,
  	[ICMP_ECHOREPLY] = ICMP_ECHO + 1,
  	[ICMP_TIMESTAMP] = ICMP_TIMESTAMPREPLY + 1,
  	[ICMP_TIMESTAMPREPLY] = ICMP_TIMESTAMP + 1,
  	[ICMP_INFO_REQUEST] = ICMP_INFO_REPLY + 1,
  	[ICMP_INFO_REPLY] = ICMP_INFO_REQUEST + 1,
  	[ICMP_ADDRESS] = ICMP_ADDRESSREPLY + 1,
  	[ICMP_ADDRESSREPLY] = ICMP_ADDRESS + 1
  };
  
  bool nf_conntrack_invert_icmp_tuple(struct nf_conntrack_tuple *tuple,
  				    const struct nf_conntrack_tuple *orig)
  {
  	if (orig->dst.u.icmp.type >= sizeof(invmap) ||
  	    !invmap[orig->dst.u.icmp.type])
  		return false;
  
  	tuple->src.u.icmp.id = orig->src.u.icmp.id;
  	tuple->dst.u.icmp.type = invmap[orig->dst.u.icmp.type] - 1;
  	tuple->dst.u.icmp.code = orig->dst.u.icmp.code;
  	return true;
  }
  
  /* Returns verdict for packet, or -1 for invalid. */
  int nf_conntrack_icmp_packet(struct nf_conn *ct,
  			     struct sk_buff *skb,
  			     enum ip_conntrack_info ctinfo,
  			     const struct nf_hook_state *state)
  {
  	/* Do not immediately delete the connection after the first
  	   successful reply to avoid excessive conntrackd traffic
  	   and also to handle correctly ICMP echo reply duplicates. */
  	unsigned int *timeout = nf_ct_timeout_lookup(ct);
  	static const u_int8_t valid_new[] = {
  		[ICMP_ECHO] = 1,
  		[ICMP_TIMESTAMP] = 1,
  		[ICMP_INFO_REQUEST] = 1,
  		[ICMP_ADDRESS] = 1
  	};
  
  	if (state->pf != NFPROTO_IPV4)
  		return -NF_ACCEPT;
  
  	if (ct->tuplehash[0].tuple.dst.u.icmp.type >= sizeof(valid_new) ||
  	    !valid_new[ct->tuplehash[0].tuple.dst.u.icmp.type]) {
  		/* Can't create a new ICMP `conn' with this. */
  		pr_debug("icmp: can't create new conn with type %u\n",
  			 ct->tuplehash[0].tuple.dst.u.icmp.type);
  		nf_ct_dump_tuple_ip(&ct->tuplehash[0].tuple);
  		return -NF_ACCEPT;
  	}
  
  	if (!timeout)
  		timeout = &nf_icmp_pernet(nf_ct_net(ct))->timeout;
  
  	nf_ct_refresh_acct(ct, ctinfo, skb, *timeout);
  	return NF_ACCEPT;
  }
  
  /* Check inner header is related to any of the existing connections */
  int nf_conntrack_inet_error(struct nf_conn *tmpl, struct sk_buff *skb,
  			    unsigned int dataoff,
  			    const struct nf_hook_state *state,
  			    u8 l4proto, union nf_inet_addr *outer_daddr)
  {
  	struct nf_conntrack_tuple innertuple, origtuple;
  	const struct nf_conntrack_tuple_hash *h;
  	const struct nf_conntrack_zone *zone;
  	enum ip_conntrack_info ctinfo;
  	struct nf_conntrack_zone tmp;
  	union nf_inet_addr *ct_daddr;
  	enum ip_conntrack_dir dir;
  	struct nf_conn *ct;
  
  	WARN_ON(skb_nfct(skb));
  	zone = nf_ct_zone_tmpl(tmpl, skb, &tmp);
  
  	/* Are they talking about one of our connections? */
  	if (!nf_ct_get_tuplepr(skb, dataoff,
  			       state->pf, state->net, &origtuple))
  		return -NF_ACCEPT;
  
  	/* Ordinarily, we'd expect the inverted tupleproto, but it's
  	   been preserved inside the ICMP. */
  	if (!nf_ct_invert_tuple(&innertuple, &origtuple))
  		return -NF_ACCEPT;
  
  	h = nf_conntrack_find_get(state->net, zone, &innertuple);
  	if (!h)
  		return -NF_ACCEPT;
  
  	/* Consider: A -> T (=This machine) -> B
  	 *   Conntrack entry will look like this:
  	 *      Original:  A->B
  	 *      Reply:     B->T (SNAT case) OR A
  	 *
  	 * When this function runs, we got packet that looks like this:
  	 * iphdr|icmphdr|inner_iphdr|l4header (tcp, udp, ..).
  	 *
  	 * Above nf_conntrack_find_get() makes lookup based on inner_hdr,
  	 * so we should expect that destination of the found connection
  	 * matches outer header destination address.
  	 *
  	 * In above example, we can consider these two cases:
  	 *  1. Error coming in reply direction from B or M (middle box) to
  	 *     T (SNAT case) or A.
  	 *     Inner saddr will be B, dst will be T or A.
  	 *     The found conntrack will be reply tuple (B->T/A).
  	 *  2. Error coming in original direction from A or M to B.
  	 *     Inner saddr will be A, inner daddr will be B.
  	 *     The found conntrack will be original tuple (A->B).
  	 *
  	 * In both cases, conntrack[dir].dst == inner.dst.
  	 *
  	 * A bogus packet could look like this:
  	 *   Inner: B->T
  	 *   Outer: B->X (other machine reachable by T).
  	 *
  	 * In this case, lookup yields connection A->B and will
  	 * set packet from B->X as *RELATED*, even though no connection
  	 * from X was ever seen.
  	 */
  	ct = nf_ct_tuplehash_to_ctrack(h);
  	dir = NF_CT_DIRECTION(h);
  	ct_daddr = &ct->tuplehash[dir].tuple.dst.u3;
  	if (!nf_inet_addr_cmp(outer_daddr, ct_daddr)) {
  		if (state->pf == AF_INET) {
  			nf_l4proto_log_invalid(skb, state->net, state->pf,
  					       l4proto,
  					       "outer daddr %pI4 != inner %pI4",
  					       &outer_daddr->ip, &ct_daddr->ip);
  		} else if (state->pf == AF_INET6) {
  			nf_l4proto_log_invalid(skb, state->net, state->pf,
  					       l4proto,
  					       "outer daddr %pI6 != inner %pI6",
  					       &outer_daddr->ip6, &ct_daddr->ip6);
  		}
  		nf_ct_put(ct);
  		return -NF_ACCEPT;
  	}
  
  	ctinfo = IP_CT_RELATED;
  	if (dir == IP_CT_DIR_REPLY)
  		ctinfo += IP_CT_IS_REPLY;
  
  	/* Update skb to refer to this connection */
  	nf_ct_set(skb, ct, ctinfo);
  	return NF_ACCEPT;
  }
  
  static void icmp_error_log(const struct sk_buff *skb,
  			   const struct nf_hook_state *state,
  			   const char *msg)
  {
  	nf_l4proto_log_invalid(skb, state->net, state->pf,
  			       IPPROTO_ICMP, "%s", msg);
  }
  
  /* Small and modified version of icmp_rcv */
  int nf_conntrack_icmpv4_error(struct nf_conn *tmpl,
  			      struct sk_buff *skb, unsigned int dataoff,
  			      const struct nf_hook_state *state)
  {
  	union nf_inet_addr outer_daddr;
  	const struct icmphdr *icmph;
  	struct icmphdr _ih;
  
  	/* Not enough header? */
  	icmph = skb_header_pointer(skb, dataoff, sizeof(_ih), &_ih);
  	if (icmph == NULL) {
  		icmp_error_log(skb, state, "short packet");
  		return -NF_ACCEPT;
  	}
  
  	/* See ip_conntrack_proto_tcp.c */
  	if (state->net->ct.sysctl_checksum &&
  	    state->hook == NF_INET_PRE_ROUTING &&
  	    nf_ip_checksum(skb, state->hook, dataoff, 0)) {
  		icmp_error_log(skb, state, "bad hw icmp checksum");
  		return -NF_ACCEPT;
  	}
  
  	/*
  	 *	18 is the highest 'known' ICMP type. Anything else is a mystery
  	 *
  	 *	RFC 1122: 3.2.2  Unknown ICMP messages types MUST be silently
  	 *		  discarded.
  	 */
  	if (icmph->type > NR_ICMP_TYPES) {
  		icmp_error_log(skb, state, "invalid icmp type");
  		return -NF_ACCEPT;
  	}
  
  	/* Need to track icmp error message? */
  	if (icmph->type != ICMP_DEST_UNREACH &&
  	    icmph->type != ICMP_SOURCE_QUENCH &&
  	    icmph->type != ICMP_TIME_EXCEEDED &&
  	    icmph->type != ICMP_PARAMETERPROB &&
  	    icmph->type != ICMP_REDIRECT)
  		return NF_ACCEPT;
  
  	memset(&outer_daddr, 0, sizeof(outer_daddr));
  	outer_daddr.ip = ip_hdr(skb)->daddr;
  
  	dataoff += sizeof(*icmph);
  	return nf_conntrack_inet_error(tmpl, skb, dataoff, state,
  				       IPPROTO_ICMP, &outer_daddr);
  }
  
  #if IS_ENABLED(CONFIG_NF_CT_NETLINK)
  
  #include <linux/netfilter/nfnetlink.h>
  #include <linux/netfilter/nfnetlink_conntrack.h>
  
  static int icmp_tuple_to_nlattr(struct sk_buff *skb,
  				const struct nf_conntrack_tuple *t)
  {
  	if (nla_put_be16(skb, CTA_PROTO_ICMP_ID, t->src.u.icmp.id) ||
  	    nla_put_u8(skb, CTA_PROTO_ICMP_TYPE, t->dst.u.icmp.type) ||
  	    nla_put_u8(skb, CTA_PROTO_ICMP_CODE, t->dst.u.icmp.code))
  		goto nla_put_failure;
  	return 0;
  
  nla_put_failure:
  	return -1;
  }
  
  static const struct nla_policy icmp_nla_policy[CTA_PROTO_MAX+1] = {
  	[CTA_PROTO_ICMP_TYPE]	= { .type = NLA_U8 },
  	[CTA_PROTO_ICMP_CODE]	= { .type = NLA_U8 },
  	[CTA_PROTO_ICMP_ID]	= { .type = NLA_U16 },
  };
  
  static int icmp_nlattr_to_tuple(struct nlattr *tb[],
  				struct nf_conntrack_tuple *tuple)
  {
  	if (!tb[CTA_PROTO_ICMP_TYPE] ||
  	    !tb[CTA_PROTO_ICMP_CODE] ||
  	    !tb[CTA_PROTO_ICMP_ID])
  		return -EINVAL;
  
  	tuple->dst.u.icmp.type = nla_get_u8(tb[CTA_PROTO_ICMP_TYPE]);
  	tuple->dst.u.icmp.code = nla_get_u8(tb[CTA_PROTO_ICMP_CODE]);
  	tuple->src.u.icmp.id = nla_get_be16(tb[CTA_PROTO_ICMP_ID]);
  
  	if (tuple->dst.u.icmp.type >= sizeof(invmap) ||
  	    !invmap[tuple->dst.u.icmp.type])
  		return -EINVAL;
  
  	return 0;
  }
  
  static unsigned int icmp_nlattr_tuple_size(void)
  {
  	static unsigned int size __read_mostly;
  
  	if (!size)
  		size = nla_policy_len(icmp_nla_policy, CTA_PROTO_MAX + 1);
  
  	return size;
  }
  #endif
  
  #ifdef CONFIG_NF_CONNTRACK_TIMEOUT
  
  #include <linux/netfilter/nfnetlink.h>
  #include <linux/netfilter/nfnetlink_cttimeout.h>
  
  static int icmp_timeout_nlattr_to_obj(struct nlattr *tb[],
  				      struct net *net, void *data)
  {
  	unsigned int *timeout = data;
  	struct nf_icmp_net *in = nf_icmp_pernet(net);
  
  	if (tb[CTA_TIMEOUT_ICMP_TIMEOUT]) {
  		if (!timeout)
  			timeout = &in->timeout;
  		*timeout =
  			ntohl(nla_get_be32(tb[CTA_TIMEOUT_ICMP_TIMEOUT])) * HZ;
  	} else if (timeout) {
  		/* Set default ICMP timeout. */
  		*timeout = in->timeout;
  	}
  	return 0;
  }
  
  static int
  icmp_timeout_obj_to_nlattr(struct sk_buff *skb, const void *data)
  {
  	const unsigned int *timeout = data;
  
  	if (nla_put_be32(skb, CTA_TIMEOUT_ICMP_TIMEOUT, htonl(*timeout / HZ)))
  		goto nla_put_failure;
  	return 0;
  
  nla_put_failure:
  	return -ENOSPC;
  }
  
  static const struct nla_policy
  icmp_timeout_nla_policy[CTA_TIMEOUT_ICMP_MAX+1] = {
  	[CTA_TIMEOUT_ICMP_TIMEOUT]	= { .type = NLA_U32 },
  };
  #endif /* CONFIG_NF_CONNTRACK_TIMEOUT */
  
  void nf_conntrack_icmp_init_net(struct net *net)
  {
  	struct nf_icmp_net *in = nf_icmp_pernet(net);
  
  	in->timeout = nf_ct_icmp_timeout;
  }
  
  const struct nf_conntrack_l4proto nf_conntrack_l4proto_icmp =
  {
  	.l4proto		= IPPROTO_ICMP,
  #if IS_ENABLED(CONFIG_NF_CT_NETLINK)
  	.tuple_to_nlattr	= icmp_tuple_to_nlattr,
  	.nlattr_tuple_size	= icmp_nlattr_tuple_size,
  	.nlattr_to_tuple	= icmp_nlattr_to_tuple,
  	.nla_policy		= icmp_nla_policy,
  #endif
  #ifdef CONFIG_NF_CONNTRACK_TIMEOUT
  	.ctnl_timeout		= {
  		.nlattr_to_obj	= icmp_timeout_nlattr_to_obj,
  		.obj_to_nlattr	= icmp_timeout_obj_to_nlattr,
  		.nlattr_max	= CTA_TIMEOUT_ICMP_MAX,
  		.obj_size	= sizeof(unsigned int),
  		.nla_policy	= icmp_timeout_nla_policy,
  	},
  #endif /* CONFIG_NF_CONNTRACK_TIMEOUT */
  };
  